New meta-analyses point to strong colorectal and breast cancer preventive benefit for vitamin D
Meta-analyses published online on February 6, 2007 in the American Journal of Preventive Medicine, and in the Journal of Steroid Biochemistry and Molecular Biology conclude that having higher blood levels of vitamin D could prevent as many as two-thirds of the cases of colorectal cancer and half of the cases of breast cancer in the United States.
The colorectal cancer analysis reviewed data from five studies that examined the association between blood levels of 25-hydroxyvitamin D and colorectal cancer risk. Blood collected from a total of 1,448 healthy participants was tested for vitamin D and the subjects were followed for up to 25 years during which cases of colorectal cancer were recorded.
Concerning the findings, coauthor Edward D. Gorham, PhD, of the University of California, San Diego (UCSD) reported, "Through this meta-analysis we found that raising the serum level of 25-hydroxyvitamin D to 34 nanograms per milliliter would reduce the incidence rates of colorectal cancer by half. We project a two-thirds reduction in incidence with serum levels of 46 nanograms per milliliter, which corresponds to a daily intake of 2,000 IU of vitamin D3. This would be best achieved with a combination of diet, supplements and 10 to 15 minutes per day in the sun."
The review included data from the Women's Health Initiative which did not find a protective effect for low dose vitamin D on seven year colorectal cancer risk, however, the researchers observed that the meta-analysis indicates that a higher dose may reduce the disease’s incidence. "Meta-analysis is an important tool for revealing trends that may not be apparent in a single study," coauthor Sharif B. Mohr, MPH noted. "Pooling of independent but similar studies increases precision, and therefore the confidence level of the findings."
The breast cancer meta-analysis included data from the Harvard Nurses Health Study and the St. George's Hospital Study, which involved a total of 1,760 women whose vitamin D levels ranged from less than 13 nanograms per liter to approximately 52 nanograms per milliliter.
"The data were very clear, showing that individuals in the group with the lowest blood levels had the highest rates of breast cancer, and the breast cancer rates dropped as the blood levels of 25-hydroxyvitamin D increased," first author Cedric F. Garland, DrPH, of UCSD stated. "The serum level associated with a 50 percent reduction in risk could be maintained by taking 2,000 international units of vitamin D3 daily plus, when the weather permits, spending 10 to 15 minutes a day in the sun."
It was noted, however, that for some individuals, any amount of sun exposure is inadvisable.
Vitamin A and vitamin D3 inhibit breast cancer cell division and can induce cancer cells to differentiate into mature, noncancerous cells. Vitamin D3 works synergistically with tamoxifen (and melatonin) to inhibit breast cancer cell proliferation.
Daily doses of vitamin A, 350,000 to 500,000 IU were given to 100 patients with metastatic breast carcinoma treated by chemotherapy. A significant increase in the complete response was observed; however, response rates, duration of response and projected survival were only significantly increased in postmenopausal women with breast cancer (Israel et al. 1985).
Breast cancer patients may take between 4000 to 6000 IU of vitamin D3 every day. Water-soluble vitamin A can be taken in doses of 100,000-300,000 IU every day. Monthly blood tests are needed to make sure toxicity does not occur in response to these high daily doses of vitamin A and vitamin D3. After 4-6 months, the doses of vitamin D3 and vitamin A can be reduced.
Monthly blood tests should include complete blood chemistry, with tests for liver function and serum calcium levels, prolactin, parathyroid hormone, and the tumor marker CA 27.29 (or CA 15.3). Additional blood tests to consider are the CEA and GGTP tests. These tests monitor the progress of therapies used and also detect toxicity from high doses of vitamin A and vitamin D3. The patient should insist on obtaining a copy of their blood workups every month.
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